Manufacturing Key Technology And Its Accuracy Evaluation Of Computer-generated Compensator For Optical Surface Test

Complex surface has important application in optical system with its unique advantages.With the continuous development of modern optical technology,higher requirements are put forward for complex surface optics,and its surface measurement technology has gradually become the key factor to control surface precision.For complex optical surfaces such as freeform surfaces,the testing method for traditional aspheric surfaces can not meet the needs of the application.Since computer-generated holograms(CGH)can generate the reference wavefront of arbitrary shape based on the diffraction theory,it can compensate various types of aberration,so it is the core device to solve complex surface detection problems.This paper will focus on the key technologies of CGH for testing complex surfaces,including the following parts:According to the manufacturing requirements of CGH,two kinds of fringe discretization models are proposed,namely the tangential segment discretization model and the DEM interpolation adaptive screening discretization model.Meanwhile,the processing data encoding of the corresponding algorithm is realized.The computational performance of two discretization models is compared and analyzed from the aspects of computational efficiency and data size.The results show that the discretization model based on DEM interpolation adaptive screening has obvious application advantages in computational efficiency,and its data size is in the machine recognition range.Aiming at the phase error introduced by DEM interpolation adaptive screening discrete process,we analyze the influence of encoding error boundary and system resolution on the actual testing results,and verify the accuracy of the discretization model by calibration experiments.The research on the evaluation of CGH testing accuracy was carried out.Based on different grating parameters,the wavefront phase and diffraction efficiency of CGH microstructures were analyzed by scalar diffraction theory and rigorous coupled wave theory.A detection system for characterizing microstructural pattern information is built,and a characterization method of CGH pattern distortion is proposed.To analyze the wavefront residual aberration introduced by pattern distortion,a distortion evaluation model based on image sampling is proposed.An evaluation method for analyzing the CGH testing error caused by the engraving error in the combined CGH preparation process is proposed.The effects of CGH substrate error,etching depth deviation,temperature pressure and surface roughness on the diffraction wavefront are analyzed,and the corresponding characterization and evaluation methods are given.For the influence of error source on wavefront residual aberration during sample design,processing and adjustment,the principle of error synthesis is given,which can be used to comprehensively evaluate the testing accuracy of CGH samples.Ultrafast laser manufacturing technology based on diffraction microstructure.The femtosecond laser manufacturing scheme for preparing the amplitude holographic microstructure was given.The process of processing micro-grooves based on femtosecond laser induced chemical etching was studied.The model of energy flow density distribution inside the fused silica was established.The triangular micro-grooves which can be used as phase-type holographic microstructures were obtained through experiments.To test the freeform mirror in the optical system,we completed the design and production of the CGH sample,and calculate the sample accuracy as RMS 9.31 nm by the error analysis model.Besides,the magnetorheological finishing was exploited based on the CGH calibration result,and the surface error of the mirror finally converges to RMS 19.6 nm.